Menthol has been used in various topical preparations as a counterirritant, as an aesthetic agent (for its fragrance), and as a plasticizer in denture adhesive compositions. Unfortunately, the aroma of menthol has been a significant hinderance to its use in any meaningful amount other than where its fragrance is desired.
In compositions containing effective counter-irritant amounts of menthol (1.25% to 16% according to the FDA monograph for menthol), the aroma from menthol can be overpowering. In compositions used for cosmetic purposes (toiletries, etc), it is used in low concentrations, typically below 0.1% by weight. One of the major drawbacks in the use of menthol for a bath product is the overpowering aroma that remains.
Various menthol esters have been prepared. Most of these esters have disagreeable odors, making them truly unsuitable for use in a topical product. These odors are as disagreeable as, or more so than, menthol itself.
Menthyl lactate is a known compound available from Haarman & Reimer GmBH (Germany) under the name FRESCOLAT, Type ML. Two thirds of its molecular weight is attributable to the menthol moiety. The manufacturer's product literature indicates that it is a "cooling agent" and that it can be used in body care and cosmetic products in which "long lasting cooling and freshness are desired." According to the manufacturer, menthyl lactate is virtually odorless, not suffering from the "mint note" that is otherwise customary in the case of other menthol derivatives. The compound is recommended for use as a flavor in concentrations of 0.005 to 0.2% and in cosmetic and other external products in concentrations ranging from 0.2 to 2.0%. The maximum recommended amount of menthyl lactate as per the product literature is therefore 2.0% by weight, which would correspond 1.3% by weight of the menthol moiety. Nowhere is there any indication or suggestion that menthyl lactate should be used as a bath product.